Rolling is generally a method of shaping metals from ingots to workable thicknesses for fabrication by passing heated material between compression rollers and under tension. Hot rolling refers to using temperatures above the recrystallization temperature of the particular metal, which leaves the processed metal ductile. Cold rolling refers to using temperatures below the recrystallization temperature for the particular metal, which adds a hardening factor to the processed metal. With the result of thinning the metal, measurement of metal thickness is usually an important part of the process. In view of the harsh environment, non-contact methods of measuring thickness are preferable.